Hydraulic servo control mechanism



United States Patent HYDRAULIC SERVO CONTROL MECHANISM Russell B. Hussey, East Longmeadow, and Marcus J.

Gottsche, Jr., Hampden, Mass, assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Nov. 29, 1961, Ser. No. 155,868 6 Claims. (Cl. 91-48) The present invention relates to a hydraulic servo control mechanism of compact construction and reduced fluid requirements.

Devices used for the drive and control of control rods in nuclear reactors have typically combined mechanical and hydraulic arrangements in which a compromise is made between compactness and reliability, as well as other advantages generally associated with each of these two general types of systems. Hydraulic drive and control systems are ordinarily preferred where extremely heavy loads exist and where there are severe space limitations. However, hydraulic systems heretofore available do not have the reliability as well as the ease of maintenance usually associated with mechanical configurations.

The present invention has to do with a hydraulic drive and control mechanism suitable for use with nuclear reactor control rods and other applications capable of obtaining benefits of heavy load capability, compactness and trouble-free operation which up to now was not thought to be possible in hydraulic systems. In accordance with this invention, a main hydraulic piston comprising the drive output is connected for feedback purposes to move a servo piston through a so-called readout rod which is connected by key and helical groove arrangement to both of the servo and main pistons. A control sleeve containing the control slots for the system encloses the servo piston while a key engaged with the servo piston as part of the mechanical feedback acts to cover or uncover the control slotsto provide the means by which the system is controlled. This arrangement permits a highly compact system which eliminates jamming and improves control over the whole system as well as other advantages as will hereinafter be made evident.

It is, therefore, a first object of this invention to pro vide a hydraulic arrangement for the drive and control of control rods in a nuclear reactor.

Another object of this invention is the provision of a hydraulic servo control mechanism utilizing mechanical feedback between the main and servo control pistons incorporating a unique fluid pressure control.

Another object is the provision of a simplified, oompact hydraulic servo control mechanism having high load capability for controlling the movements of the main drive piston.

Still another object of this invention is the provision of a fail-safe hydraulic servo control mechanism which minimizes the possibilities of binding and whose performance will not deteriorate due to mechanical wear.

Other objects and advantages of this invention will hereinafter become more apparent from a reading of the following description of a preferred embodiment of this invention which is illustrated in the accompanying drawing showing an isometric view partially cut away and schematized.

Illustrated in the FIGURE is a portion of a pressure vessel 12 which may be part of a nuclear reactor whose control rods are to be driven and controlled by the hydraulic drive mechanism 10 of this invention. Of course, mechanism .10 may be used in other applicationswhere it would be suitable. It should be pointed out at this point that the hydraulic mechanism 10 illustrated in the figure is oriented with the top at the left extending to the right,

Patented Sept. 17, 1963 ice or downwardly. Hence, in its customary and expected utilization, the unit would be vertically mounted, the axis from left to right in the drawing extending from top to bottom.

Extending up from the top of pressure vessel 12 is a cylindrical pressure vessel head 14 which is closed off at the top as shown. A so-called closed loop system 16 for providing system pressure is provided. System 16 provides hydraulic fluid under desired pressure through a tube 18 into pressure vessel head 14. Suction or return of fluid from the interior of pressure vessel 12 is provided through a conduit 22 extending from vessel 12 to system 16. Closed loop system 16 is a conventional arrangement for providing fluid pressure and would generally include a pump, means to drive the pump and quite often a reservoir for storing the fluid and controlling the fluid pressure. The fluid used here may be any suitable hydraulic fluid, and in the case of a reactor, the cool-ant within the reactor itself is quite often suitable for this purpose.

Also extending up from the top of vessel 12 into pressure vessel 12 are a pair of drive shafts 24 and 26 connected to pinion or drive gears 23 and 32, respectively. Drive shaft 24 is driven through a magnetic coupling arrangement 34 by a piston control motor 36 while drive shaft 26 is similarly driven through a magnetic coupling arrangement 38 by a scram motor 42, for a purpose to be later described. Clutches not illustrated may also be provided in these driving arrangements. While the trans mission arrangements, generally designated as 34 and 38, may be conventional in nature if suitable for the particular application, they are illustrated as magnetic couplings to avoid openings in the reactor containment. The purpose of these drive arrangements is for the control of mechanism .10. Their specific connection and mode of operation will be described further below.

Within vessel 12 is a cylindrical main support mem- 'ber 44 having an extension threadably engaged into pressure vessel head 14 as illustrated. Extension 46 is also provided with internal threads 48 for engagement with a bearing 52 which supports rotatably one end of a hollow so-called readout rod 54. The other end of readout rod 54 is supported :slidably in a bearing 56. The latter is supported by the main power piston 58 which is rigidly connected as indicated by ring weld 62. to hearing 56. A key 64 mounted through bearing 56 is located to engage with a drive helical slot 66 along the outer surface of readout rod 54. By this arrangement, movement of power piston 58 along the axis of readout rod 54 will cause readout rod 54 to rotate. Therefore, the rotational position of rod 54 will indicate the axial position of power piston 58 in mechanism 10. It should be noted briefly here that power piston 58 is connected by way of a ring extension 68 to a hollow piston rod 72 which extends downwardly therefrom and is connected ultimately to the load or control rod (not shown). Piston rod 72 is provided with two pairs of oppositely facing slots 74 for a purpose to be later described.

At this point it will be seen that fluid pressure delivered from system 16 through tube 18 into the interior of pressure vessel head 14 enters an end opening (not shown) in readout tube 54, travels the length of this tube, and exits to within piston tube 72. The fluid under pressure leaves the interior of piston rod 72 through slots 74 and pressurizes one side of power piston 58 as indicated by arrows A.

Stationary main support member 44 contains a pair of I oppositely facing, vertically elongated slots 76, only one shown. In the annular space formed between support member 44 and readout rod 54 is located the servo piston 78 which has attached to it on opposite sides a pair of large servo piston keys 82 only one of which is illustrated.

One or mores crews 83 may be used to attach keys 82 to the outer surface of servo piston 78. Each servo piston key 82 is rectangularly shaped to slide within a vertical slot 76 as illustrated. Each servo piston key 82 is provided with a key follower 84 to slide within a helical keyway 86 formed in the outer surface of readout rod 54. It will be seen that rotation of readout rod 54 will cause servo piston 78 to slide axially as a result of this arrangement.

Main support member 44 is provided with an expanded internal section 88 below and spaced from servo piston 78. A plurality of small holes 92 through the wall of rod 54 are provided in the annular space between piston 78 and section 88 to provide access for hydraulic fluid so as to pressurize the annular space directly below servo piston 78. The hydraulic fluid under system pressure will tend to move servo piston 78 to the left, or upward, in the same direction that system pressure tends to move main piston 58 as indicated by arrows A.

Surrounding stationary main support member 44 is a cylindrical control sleeve 94 which is keyed to member 44 (by means not illustrated) to permit axial movement only with respect to member 44. Control sleeve 94 is provided with a pair of two oppositely facing control slots 96, only one of which can be seen. Each of slots 96 is in alignment with a vertical slot 76 so that the lower end of key 82 partially covers a control slot 96 for a reason to be later explained. Control sleeve 94 is also provided with a pair of helical keyways 98 along the outer surface thereof for engagement with a pair of keys 102 mounted on the inside of a gimbal drive ring 104. Gimbal drive ring 104 is pivoted by a pair of pins 106, one of which can be seen, to a control sleeve drive gear tube 108. Tube 108 is cylindrical in shape and is provided with a plurality of openings or holes 112 to avoid interfering with fluid flow therein. Tube 108 is supported at each end by a pair of roller bearings 114 and 116, respectively. The upper end of control sleeve drive gear tube 108 terminates in a control sleeve drive gear 118 which engages with drive pinion 28, previously identified. Hence, the connection between pinion 28 and control sleeve drive gear 118 makes it possible to position selectively control sleeve 94 axially and hence the position of control slot 96 with respect to the lower edge of servo piston key 82. By positioning control slot 96 relative to the end of key 82, it is possible to control the flow of fluid through control slots 96 and, as will be seen later, ultimately position the control rod or load which is connected to the bottom of piston 72. An anti-backlash spring 122 is provided between drive gear 118 and the control sleeve 94 which has a stop 124 for this purpose. Spring 122 also returns control sleeve 94 to rod bottom position during a scram which is accomplished by a separate control arrangement as will be described below.

Surrounding main piston 58 is a cylinder 126 in which main power piston 58 slides. Cylinder 126 is threadably engaged at one end to a ring 128 which is provided with an internally threaded bearing member 132 for supporting readout rod 54 as illustrated. The other end of cylinder 126 terminates in a closed wall 127 having a flanged portion 127a, for a purpose to be later described. Returning to the other end of cylinder 126, an adjustment and locking nut 134 is provided over bearing 132 immediately adjacent ring 128 to support bearing 116 previously described, and also to adjust and lock cylinder 126 in place. Cylinder 126 is provided with a plurality of displacement slots 136 above power piston 58 to insure that the upper side of piston 58 is not pressurized with fluid and to prevent the entrapment of fluid therein. Cylinder 126 is provided, below power piston 58, with a plural ity of scram openings 138 which are oifset from scram sleeve dump ports 142 located in a scram sleeve 144 which encloses cylinder 126. Openings 138 in cylinder 126 and ports 142 in sleeve 144 have the same vertical position, but they are staggered rotationally to prevent the loss of fluid pressure below power piston 58. Scram sleeve 144 is cylindrical in shape and is connected through a tube 145 to a scram sleeve drive gear 146 which is engaged to pinion 32 which was previously described. Tube 145 is pierced with a plurality of holes 147, to prevent entrapment of fluid, and fits over an expanded section or shoulder 144a of sleeve 144.

A scram torsion spring 148 connecting scram sleeve 144 and flange 127a is provided to rotate scram sleeve 144 to a position where ports 130 and 142 interconnect to dump high pressure fluid.

For normal operation, scram motor 42 is energized to overcome spring 148 and rotate scram sleeve 144 to a position, where ports 138 and 142 are staggered, and thereafter hold this position. When it is desired to scram the control mechanism 10, a clutch (not shown) will be actuated to disengage the transmission arrangement 38 and allow scram spring 148 to rotate scram sleeve 144 to a position where scram sleeve ports 142 are aligned with openings 138 in cylinder 126 thereby relieving pressure from below power piston 58 and permitting the control rods, or other load, to drop under the force of gravity.

In the control operation of the apparatus just described, pressurized fluid is delivered from closed loop system 16 through conduit 18 into the interior of pressure vessel head 14 as previously described. The pressurized fluid flows through hollow readout rod 54 into piston rod 72 and out through rod slots 74 to apply pressure to power piston 58 as indicated by arrows A. Someof the pressurized fluid is forced out through openings 92 in readout rod 54 to direct a vertical upward force against servo piston 78, also in the direction of arrows A. Servo piston 78 is coupled through readout rod 54 to main piston 58 by means of helical keyways 66 and 86 as previously described. All backlash is removed by the continous hydraulic force which urges piston 78 in a vertical upward direction. The mechanical linkage between main piston 58 and servo piston 78 including readout rod 54 acts as a restraining stop on servo piston 78 during upward movement of main piston 58. Thus, readout rod 54 becomes torsionally loaded, and in the particular embodiment illustrated, this is approximately in.-lbs. Helical keyways 86 and 66 are designed with suflicient clearance to eliminate completely any possibility of jamming, as in understood in the art. Hence, movement of main piston 58 in response to fluid pressure, upwardly for example, results in like movement of servo piston 78. The ratio of motion between main piston 58 and servo piston 78 is approximately thirty-eight to one in the particular configuration illustrated so that a three inch motion of the servo piston 78 represents the full stroke of main piston 58.

In order to control the movement and location of the control rod or other load (not illustrated) connected to piston rod 72, motor 36 would be energized to turn pinion 28 and rotate the control sleeve drive gear 118 to move gimbal drive ring 104 and hence control sleeve 94 axially. With the control sleeve 94 moved axially torod or load bottom, extreme right, position leakage control slots 96 will be fully opened and excessive leakage through these slots will result in insufficient system pressure to actuate main piston 58. Axial upward movement of control sleeve 94 in response to rotation of piston control motor 36 will reduce the leakage area of control slots 96 as control sleeve 94 moves upwardly to cause servo piston key 82 to close off a portion of control slots 96. This will result in an increased system pressure sufficient to move main piston 58 upward. If at some particular point, upward motion of control sleeve 94 is stopped by halting the rotation of motor 36, motion of main piston 58 and that of coupled servo piston 78 will continue until the change in control slot area and leakage causes reduction of system pressure to a holding value. In a similar fashion, downward movement of control sleeve 94 will increase the leakage area of control slots 96 which will result in a decrease in system pressure suflicient to cause downward movement in main piston 58.

When downward motion of control sleeve 94 is stopped, main piston 58 and the coupled servo piston 78 motions will continue until the change in control slot area and leakage cause an increase in system pressure to a holding value. During downward motion of main piston 58 the mechanical linkage between main piston 58 and servo piston 78 applies a force on the latter to overcome the hydraulic force and thereby moves servo piston 78 downward.

By this arrangement, avoiding shaft seals altogether and without backlash, it is seen that simple, eflective and close control is exercised over the control rod or other load connected to piston rod 72.

Readout rod 54, whose rotational position is indicative of the axial location of piston rod 72, may be terminated within pressure vessel head 14 in any convenient fashion, provided, there are openings for the hydraulic fluid. A magnetic coupling (not shown) may be utilized to detect the orientation of readout rod 54 and hence the location of piston rod 72. It should be noted that mechanism may be oriented in other than a vertical position for the movement of piston rod 72 provided that other than gravitational means are used to insure proper movement of the load when system pressure drops. While not illustrated, a snubbing arrangement may conveniently be incorporated into piston rod 72 and cylinder 126. Also, a gimbal driving means similar to the gimbal drive for control sleeve 94 except for size may be used between readout rod 54 and the servo piston keys 82. It may be fitted into the annular opening above servo piston 78. Another gimbal drive between main piston 58 and readout rod 54 for which a second helical keyway must be provided on readout rod 54 may also be incorporated. The mechanism is fail-safe and non-jamming and yet is compact. Being substantially all hydraulic there will be no performance deterioration due to mechanical wear.

It is thus seen that there has been provided a unique and almost completely hydraulic arrangement for obtaining the control and drive of a control rod or other load.

While only a preferred embodiment of this invention has been illustrated and described, it is understood that within the principles of this invention many variations may be made without departing from the scope thereof as set forth in the appended claims.

What is claimed is:

1. A hydraulic servo "control mechanism comprising, in combination, a source of fluid pressure, main piston means slidable in axial directions, servo piston means spaced from said main piston means also slidable in axial directions, said servo and main piston means each exposed on one side to said fluid under pressure for being urged in one direction, means transferring a biasing force to said main piston means to urge the latter in -a direction opposite to that urged by said fluid under pressure, mechanical means interconnecting said main and servo piston means (1) to restrain the latter to move simultaneously with the movement of the former in response to an excess of fluid pressure over said biasing force and (2) to drive said servo piston means back in response to movement of said main piston means when said biasing force exceeds fluid pressure on the latter, control means movable with respect to said servo piston means, control slots formed in said control means to discharge fluid acting on said servo and main piston means thereby effecting a decrease in fluid pressure, means attached to said servo piston means for adjustably blocking fluid flow through said control slots as a result of relative movement of said control means and servo piston means, and means for selectively adjusting the position of said control means to alter flow through said control slots and hence to change fluid pressure on said servo and main piston means to cause a change in force acting on said main piston means as a result of change in fluid pressure acting thereon.

2. The hydraulic servo control mechanism of claim 1 in which fluid pressure acting on said main and servo piston means urges said servo piston in the direction of uncovering said control slots thereby causing a decrease in fluid pressure and consequent lessened force acting on said servo and main piston means.

3. The hydraulic servo control mechanism of claim 2 in which means are provided to bias said control means in a direction tending to unblock said control slots thereby eliminating backlash between said servo and main piston means.

4. The hydraulic servo control mechanism of claim 3 in which said mechanical means includes a hollow rod extending through said servo and main piston means, said fluid under pressure being delivered to said servo and main piston means through said hollow rod.

5. The hydraulic servo control mechanism of claim 3 in which said mechanical means consists of a hollow rod extending through said servo and main piston means, the mechanical connection between each of said servo and main piston means and said hollow rod being formed by helical keyways on the outer surface of said rod and follower keys attached to both said servo and main piston means for converting slidable movement of said main piston means to rotary movement of said rod and converting rotary movement of said rod to slidable movement of said servo piston means.

6. The hydraulic servo control mechanism of claim 1 in which means are provided to override the operation of the control arrangement and dump all fluid within said mechanism and thereby bring said main piston means into unopposed movement in a direction opposite to that urged by said fluid under pressure.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A HYDRAULIC SERVO CONTROL MECHANISM COMPRISING, IN COMBINATION, A SOURCE OF FLUID PRESSURE, MAIN PISTON MEANS SLIDABLE IN AXIAL DIRECTIONS, SERVO PISTON MEANS SPACED FROM SAID MAIN PISTON MEANS ALSO SLIDABLE IN AXIAL DIRECTIONS, SAID SERVO AND MAIN PISTON MEANS EACH EXPOSED ON ONE SIDE TO SAID FLUID UNDER PRESSURE FOR BEING URGED IN ONE DIRECTION, MEANS TRANSFERRING A BIASING FORCE TO SAID MAIN PISTON MEANS TO URGE THE LATTER IN A DIRECTION OPPOSITE TO THAT URGED BY SAID FLUID UNDER PRESSURE, MECHANICAL MEANS INTERCONNECTING SAID MAIN AND SERVO PISTON MEANS (1) TO RESTRAIN THE LATTER TO MOVE SIMULTANEOUSLY WITH THE MOVEMENT OF THE FORMER IN RESPONSE TO AN EXCESS OF FLUID PRESSURE OVER SAID BIASING FORCE AND (2) TO DRIVE SAID SERVO PISTON MEANS BACK IN RESPONSE TO MOVEMENT OF SAID MAIN PISTON MEANS WHEN SAID BIASING FORCE EXCEEDS FLUID PRESSURE ON THE LATTER, CONTROL MEANS MOVABLE WITH RESPECT TO SAID SERVO PISTON MEANS, CONTROL SLOTS FORMED IN SAID CONTROL MEANS TO DISCHARGE FLUID ACTING ON SAID SERVO AND MAIN PISTON MEANS THEREBY EFFECTING A DECREASE IN FLUID PRESSURE, MEANS ATTACHED TO SAID SERVO PISTON MEANS FOR ADJUSTABLY BLOCKING FLUID FLOW THROUGH SAID CONTROL SLOTS AS A RESULT OF RELATIVE MOVEMENT OF SAID CONTROL MEANS AND SERVO PISTON MEANS, AND MEANS FOR SELECTIVELY ADJUSTING THE POSITION OF SAID CONTROL MEANS TO ALTER FLOW THROUGH SAID CONTROL SLOTS AND HENCE TO CHANGE FLUID PRESSURE ON SAID SERVO AND MAIN PISTON MEANS TO CAUSE A CHANGE IN FORCE ACTING ON SAID MAIN PISTON MEANS AS A RESULT OF CHANGE IN FLUID PRESSURE ACTING THEREON. 